The chance of getting pregnant in each menstrual cycle (each month) is very high. However, it may take a long time to conceive, even if everything is looks normal, because some may just be a bit weak. Eight out of every ten women trying for a baby will fall pregnant within the first six months. Women who do become pregnant without any medical assistance generally do so within 8 months of trying. It is common for couple to seek help and advice if there is difficulty conceiving. Overall, around 15 per cent (one in six) of all couples will seek help. The point at which they may want to seek help will depend on various factors. For example, if they are over 35 years of age or if they have any worrying symptoms, such as infrequent period and so on, the couple should seek help after about six months of trying.

1. The woman Ovulation is the end of a complicated series of events leading to the release of an egg from the ovary. If that egg is fertilized by a sperm and implants in the lining of the womb (endometrium), a pregnancy has started. All of a woman's eggs will already be present when she is born. From the early years of childhood, she starts to lose eggs, but it is calculated that a woman aged 50 still has about 1000 of her eggs left. A woman's cycle begins with a hormonal signal from the pituitary gland at the base of the brain. It releases a follicle stimulating hormone (FSH), which stimulates the ovaries. FSH stimulates a group of about 20 follicles on the surface of the ovary to grow. Within the follicles are the developing eggs. Another hormone, estrogen, is produced by the ovary and in response to increasing estrogen levels, the largest follicle continues to develop. This is why most pregnancies result in only a single baby. Another hormone, utilizing hormone (LH), also produced by the pituitary gland, causes the follicle in the ovary to release the egg. This release of the egg (or ovum) is called ovulation. After ovulation, the empty follicle forms a structure called the corpus luteum which produces a hormone called progesterone. Levels of progesterone rise after ovulation and prepare the womb to receive a fertilized egg (embryo). Fertilization by a sperm, if this occurs, takes place in the Fallopian tube, which then moves the early embryo along towards the womb itself. If the egg is not fertilized, or the embryo does not implant in the womb, the progesterone levels fall and a period starts. The whole cycle then begins again.

2. The man The man's role in conception is the production and ejaculation of sperm cells. To fertilise an egg, a man must be capable of producing adequate numbers of swimming (motile) sperm. Only a few of these sperm cells will in the end reach the egg, and only one will actually enter and fertilise it. During puberty, the testes become active and start to produce sperm. From his teens until about the age of 70, a man will typically produce 5,000 sperm cells every minute. Ejaculation produces semen, which is a mixture of two per cent sperm cells and 98 per cent liquid produced by the glands in the testes. Production of sperm is under the control of FSH and LH, the same hormones that control the woman's fertility.